The proposed work is designed to elucidate the mechanism of action and metabolism of 2-amino-1,3,4-thiadiazole (ATDA) and its derivatives. Labeled and unlabeled ATDA and three of its derivatives will be prepared. An in vitro or in vivo system derived from mice or L1210 cells capable of producing sufficient quantities of thiadiazole-containing nucleotides for structural analysis will be identified. If such a system can not be obtained, NAD+ analogs containing thiadiazoles will be prepared utilizing NADase and then hydrolyzed with nucleotide pyrophosphatase to yield thiadiazole mononucleotides. These fraudulent nucleotides will be tested for inhibition of IMP dehydrogenase purified from L1210 cells. The structure of the ATDA-containing nucleotide present in L1210 cells will be determined, as will the structures of the major urinary metabolites of ATDA.